Dampening fluid pump and metering apparatus for offset printing press

ABSTRACT

Dampening fluid is successively pumped in metered, very small individual volumes by a series of pump units to sprayers which nebulize the fluid and discharge the same onto a roll of an offset printing press. Each pump unit has as its primary component a relatively small, resilient, tubular element which positively displaces a predetermined volume of fluid to its sprayer during each operating cycle by successively constricting and expanding its flow passage when a compressive force is applied and relaxed to the element in the direction of fluid flow therethrough. A bubble-releasing and guiding channel in each element is open along its length to the flow passage of the element and has an entry at the inlet end of the element configured to avoid the formation of a ledge or the like upon which bubbles could collect and thereby expand and contract during operation of the element to appreciably affect the volume of fluid displaced by the element. Individual lever arm control assemblies for the pumping elements of the units are provided with adjustable limit stops to permit metering of the fluid from each element independently of all others.

United States Patent [191 Glaser Oct. 9, 1973 [21] Appl. No.: 268,735

Primary ExaminerAllen N. Knowles Assistant Examiner-Gene A. ChurchAttorney-Schmidt, Johnson, Hovey 8; Williams [57] ABSTRACT Dampeningfluid is successively pumped in metered, very small individual volumesby a series of pump units to sprayers which nebulize the fluid anddischarge the same onto a roll of an offset printing press. Each pumpunit has as its primary component a relatively small, resilient, tubularelement which positively displaces a predetermined volume of fluid toits sprayer during each operating cycle by successively constricting andexpanding its flow passage when a compressive force is applied andrelaxed to the element in the direction of fluid flow therethrough. Abubble-releasing and guiding channel in each element is open along itslength to the flow passage of the element andhas an entry at the inletend of the element configured to avoid the formation of a ledge or thelike upon which bubbles could collect and thereby expand and contractduring operation of the element to appreciably affect the volume offluid displaced by the element. Individual lever arm control assembliesfor the pumping elements of the units are provided with adjustable limitstops to permit metering of the fluid from each element independently ofall others.

25 Claims, 9 Drawing Figures Patented Oct. 9, 1973 3,764,070

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Patented Oct. 9, 1973 3,764,070

2 Sheets-Sheet 2 DAMPENING FLUID PUMP AND METERING APPARATUS FOR OFFSETPRINTING PRESS This invention relates to fluid supply apparatus which isespecially suited for the pumping and metering of dampening fluid usedto wet the printing plate of offset printing presses so non-printingareas will repel ink.

In an offset printing process, print quality is highly sensitive tosupply of water to the system. Effective control over the quantity ofwater delivered to the printing plate is difficult to maintain, however,because although only very small amounts of water must be delivered tothe plate, the supply must be capable of being infinitely varied toaccommodate different ink densities, types of ink, total ink coverage,press speed and similar highly variable factors.

Therefore, one of the most important objects of this invention is toprovide apparatus for repeatedly supplying very small yet precisevolumes of dampening fluid to the rolls of an offset printing presswhereby print quality may be maintained on an exceptionally high level.

Another importnat object of the instant invention is to provideapparatus as aforesaid which, although displacing only a very smallvolume of fluid during each operating cycle, is capable of accuratevariation of even this small fluid volume so that print quality may beaccurately controlled to an even greater degree.

An additional important object of the present invention is to providedampening apparatus having a simple, positive displacement, resilient,tubular'pumping elementor plug in which a minute yet precise pumpingaction is effected by successive constriction and expansion of its fluidpassage in a transverse direction when a compressive force is applied tothe plug in the direction of fluid flow therethrough, thereby permittingaccurate metering of the volume of fluid displaced by simply controllingthe extent of compression and expansion of the plug.

Another important object of the present invention is the provision ofpumping apparatus as aforesaid wherein the provision of a directingchannel or way for bubbles at the inlet end of the passagethrough theresilient element eliminates the formation ofa ledge at such inlet endwhich might otherwise collect bubbles that would be subject to expansionand compression during the pumping action. If bubbles were allowed tocolledt they would appreciably affect the amount of fluid displaced bythe pump because of the relatively small volume of dampening liquiddelivered by the apparatus during each cycle. I

An additional important object of the instant invention is to providedampening apparatus as aforesaid, which utilizes a pneumatically poweredsprayer for discharging a fine mist onto the roll or other surface to bedampened, wherein dampening fluid is delivered to the sprayer by virtueof a positive displacement, resilient pumping element, without theassistance of air pressure, so that the amount of fluid displaced duringeach pumping cycle may be very accurately metered by the use ofmechanical, readily adjustable mechanism which controls the extent ofcompression and expansion of the element.

A further important object of the invention is to provide dampeningapparatus as set forth above having a series of sprayers and pumpingelements therefor, each of which is provided with a non-complex, yethighly accurate control assembly which allows compression and expansionof each element to be individually controlled independently of all otherelements, whereby to provide local control of dampening fluidapplication across the full width of the roll or surface being dampened.

Another important object of the instant invention is the provision ofsuch a control assembly for each pumping element which not only affordsprecise calibration for accurate regulation of the fluid displaced byeach element, but, in addition, is designed for convenient and rapidinstallation and removal in order to provide access to the corresondingpumping elements for service or replacement thereof.

In the drawings:

FIG. 1 is an essentially schematic view of the pumping and meteringapparatus of the present invention shown in conjunction with rolls of anoffset printing press;

FIG. 2 is an enlarged, fragmentary and elevational view of the appratus;

FIG. 3 is an enlarged, fragmentary plan view of apparatus;

FIG. 4 is a plan view similar to FIG. 3 with the apparatus rotatedninety degrees from its orientation of FIG. 3;

FIG. 5 is an enlarged, fragmentary cross-sectional view of the apparatustaken along line 5-5 of FIG. 4;

FIG. 6 is an enlarged, fragmentary cross-sectional view through thesprayer head of the apparatus taken along line 6-6 of FIG. 5;

FIG. 7 is an enlarged, detail view of an individual pump unit of theapparatus, showing the piston thereof fully extended;

FIG. 8 is a cross-sectional view through the unit taken along line 8-8of FIG. 7; and

FIG. 9 is an enlarged, detail view of the pumping unit similar to FIG.7, but with the piston thereof forced into the unit to compress theresilient pumping element thereof.

The apparatus 10 is shown in FIG. 1 in its normal inclined dispositionfor spraying dampening fluid onto the rolls of an offset printing press.Apparatus 10 is mounted directly on the press and may be disposed todirect a mist of the damping fluid onto a vibrator roll 12 of the presswhich ultimately transfers the fluid to theplate cylinder 14 via anintermediate form roll 16. Ink may be supplied to plate cylinder 14 by adistributor roll 18, a second vibrator roll 20, and a pair of form rolls22. If desired, a small intermediate transfer roll 24 may be providedbetween form rolls l6 and 22 in order to supply a small quantity of inkto roll 12, such that spray from apparatus 10 is actually applied to thesurface of ink film on roll 12 before the fluid is transferred to platecylinder 14.

Apparatus 10 includes a main elongated, rectangular head 26 having aseries of sprayers 28 spaced longitudinally along head 26. Alongitudinally extending air line 30 (FIG. 6) formed internally of head26 has an external fitting 32 (FIGS. 3 and 4) which is adapted forconnection to a source of pressurized air (not shown). An annular inlet34 for each sprayer 28 communicates line 30 with the nozzle 36 of eachsprayer 28, and a fluid receiving bore 38 in head 26 for each sprayer 28communicates with nozzle 36 and houses a reciprocable, spring-locatedcleaning pin 40.

A plurality of spaced apart dividing plates 42 are secured to head 26along the length of the latter to define individual bays which containthe means for supplying fluid to each of the sprayers 28. Within eachbay is a pump unit 44 forming a part of apparatus 10, having a pumpcylinder 46 which is partially received by head 26. Each cylinder 46 hasan elongated internal chamber which is closed at one end by an end wall48 having an outlet port 50 therein which communicates with thecorresponding bore 38 via a short line 52. A stationary abutment block54 lies against the end wall 48 within the chamber of cylinder 46, andhas a counterbored outlet 56 therein aligned with port 50 which has acheck valve 58 biased by a coil spring 60 away from port 50. Thediameter of outlet 56 in the area of the valve 58 is such that fluid maypass around the periphery of valve 58 for flow through outlet 56 towardport 50.

Also contained within the chamber of cylinder 46 is an elongatedcylindrical, resilient, pumping element or plug 62 having a central boreor passage 64 extending longitudinally therethrough. Passage 64 issmaller in diameter than the counterbored area of outlet 56, and thehead of valve 58 is coneshaped such that valve 58 is biased into theoutlet end of passage 64 by spring 60 to normally close passage 64. Theopposite inlet end of passage 64 is provided with a directing channel orway 66 which leads from the inlet end of passage 64 toward the outletend thereof, but terminatesshort of outlet 56. Channel 66 progressivelydiminishes in size as outlet 56 is approached and, as seen in FIG. 8,channel 66 tangentially intersects passage 64 on opposite lateral sidesthereof.

Also normally housed within cylinder 46 of each pump unit 44 is areciprocable piston 68 forming a part of mechanism 70 for manipulatingpumping element 62. A counter-bored inlet 72 in piston 68 communicateswith passage 64 and has a check valve 74 normally biased into sealingengagement with an O-ring 76 by a coil spring 78. The head of valve 74is coneshaped to form a tight seal with O-ring 76 when valve 74 isseated thereagainst, but the periphery of valve 74 is not in tightengagement with the proximal counterbored area of inlet 72 so that fluidcan, therefore, escape around valve 74 when the latter is unseated fromO- ring 76. The counterbored area of inlet 72 is of greater diameterthan passage 64 such that the inlet end of the latter is encircled bythe corresponding end of inlet 72. Note, however, that the entrance tochannel 66 extends, transversely of passage 64, along the interfacebetween piston 68 and plug 62 from within the dimensional limits of thecounter-bored area of inlet 72 to outside of the same whereby toeliminate the existence of a ledge or the like or plug 62 at thislocation. Inlet 72 is coupled via a short, flexible line 80 to a supplyline 82 common to all of the units 44 and coupled with a source ofdampening fluid (not shown).

Mechanism 70 for operating each pump unit 44 includes, in addition toeach piston 68, a common drive shaft 84 hournaled by bearings in theplates 42 for rotation by a motor and chain assembly 86 supported by alarge plate 88 at one end of head 26. A series of eccentrics 90 areaffixed to shaft 84, there being one eccentric 90 between each adjacentpair of plates 42, and a control assembly 92 is provided for each unit44 for transmitting driving power from the corresponding eccentric 90 tothe corresponding piston 68. The main component of each control assembly92 is a swingable lever arm 94 pivoted intermediate its ends by anexternal fulcrum shaft 96 which projects from the adjacent plate 42.Each arm 94 has a rocker 98 thereon disposed below fulcrum 96 whichbears against piston 68 during operation and has a suitable opening forclearing the short, flexible line 80. The upper end of each arm 94 isprovided with a follower bolt 100 whice is threadably received by arm 94for adjustment toward and away from eccentric 90, there being a lockingnut 102 provided on bolt 100 for retaining the latter in any one of anumber of selected positions.

A bar 104 extending across the plates 42 is tied to the latter and toplate 88 and threadably carries a series of lower adjusting screws 106,one for each arm 94, for controlling the limits of swinging of thecorresponding arms 94 to thereby control the length of stroke of thecorresponding pistons 68. The innermost end of each limit screw 106 isengageable with a flat, impact area 108 on the lowermost end of arm 94during swinging of the latter to thereby determine its limits. As shwonbest in FIG. 5, an enlarged, indicia-bearing poriion 1 10 may beprovided on each limit screw 106 for cooperating with a suitable pointer112 or equivalent structure on bar 104 for visually indicating thelength of stroke which has been selected for piston 68 upon actuation ofapparatus 10.

OPERATION As shown in FIG. 1, apparatus 10 is normally inclined at anattitude of 45 so that dampening fluid supplied to sprayers 28 is pumpeduphill, thereby minimizing the formation of bubbles within the variousflow lines and passages leading to sprayers 28. Assuming, for purposesof illustration, that apparatus 10 is initially in the conditionillustrated by FIGS. 5 and 7, actuation of the motor and chain assembly86 causes drive shaft 84 to simultaneously rotate all of the eccentrics90. As each eccentric rotates from its FIG. 5 position with the followerbolt bearing thereagainst, its corresponding arm 94 is swung in acounterclockwise direction viewing FIG. 5 as the end of arm 94 forcespiston 68 inwardly against plug 62. The rocking connection betweenrocker 98 and the outer face of piston 68 permits longitudinal movementof piston 68 at this time, while arm 94 swings in its arcuate path oftravel.

Inward movement of piston 68 toward its position of FIG. 9 causes theinlet valve 74 to seat firmly against O-ring 76 and thereby preclude themovement of fluid in either direction through inlet 72. However, becauseabutment block 54 prevents movement of plug 62 in the direction of fluidflow through passage 64 and because cylinder 46 precludes outwardexpansion of plug 62 transversely of such direction of fluid flow,passage 64 is forced to constrict intermediate its ends and therebyforce any fluid contained therewithin against outlet valve 58. Thus, asshown in FIG. 9, valve 58 is pushed out of its seating relationship withthe outlet end of passage 64 to allow fluid within the latter to exitaround valve 58, through outlet 56, port 50 and into bore 38 by way ofline 52. The volume of fluid thus displaced travels through bore 38 .andinto nozzle 36 of sprayer 28 where it is nebulized by air flowing intothe latter from the annular inlet 34 for issuance as a fine mist ontothe vibrator roll 12, as shown in FIG. 1.

As shaft 84 then continues its rotation, the arms 94 are allowed toreturn to their initial positions, each swinging in a clockwisedirection as their compressed plug 62 seeks to return to its normal,uncompressed condition. As this expansion stroke of the piston 68 takesplace, outlet valve 58 is returned to its sealing engagement withpassage 64 by virtue of spring 60 and the vacuum created within passage64. Simultaneously, inlet valve 74 is unseated from O-ring 76 by thevacuum created within passage 64 to thereby allow a volume of fluid toflow past O-ring 76 and around valve 74 into passage 64 in preparationfor the next compresion stroke of piston 68. When piston 68 reaches itslimit of extension, determined either by the throw of eccentric 90 orthe selected setting for adjustable limit screw 106, the loading ofpassage 64 with fluid ceases. At this time, the components are againdisposed as shown in FIGS. 5 and 7 in preparation for the nextcomprssion stroke of piston 68.

By way of example, it is contemplated that each piston 68 may have astroke of from zero to 0.025 inches with a normal stroke (depending uponthe particular ink conditions at hand) being approximately 0.005 inches.The diameter of each passage 64 is preferably from five-eighths toseven-sixteenths inches. Accordingly, it can readily be seen that thevolume of fluid pumped by each plug 62 during each pulse or cycle isextremely small so that only a fine mist is discharged to the presssystem as opposed to a high volume, heavy spray. The unique design andmode of operation of plugs 62 permit such small quantities to bedisplaced without an attendant sacrifice in the degree of precisionrequired for quality printing.

The bubble channel or way 66 of each plug 62 plays an important role inthe displacement of consistently uniform amounts of fluid to thecorresponding sprayer 28, such role being especially significant becauseof the small volume of fluid ejected by plugs 62. To this end, thepresence of one or more bubles trapped between inlet and outlet valves74 and 58, respectively, during each operating cycle would appreciablyaffect the volume of fluid displaced as the bubbles expanded andcontracted along with plug 62. Because of the attitude of apparatus 10,bubbles 'within the system move along the upper reaches of lines 80, 82and inlet 72 and would normally become trapped against the outside ofplug 62 adjacent the inlet end of passage 64 because of the decreaseddiameter of the latter with respect to inlet 72. However, bubble channel66 eliminates the existence of any collecting ledge on plug v62 for thebubbles such that the same are directed back into passage 64 for flowtherethrough with their corresponding volume of fluid withoutappreciably affecting the true volume of fluid dispensed. Withoutchannel 66, bubbles could collect over a prolonged period of operationand thereby have a significant effect on the amount of fluid displaced,and hence on the quality of printing performed by the press.

The provision of the adjustable limit screw 106, with its indiciaportion 110 and the adjustable follower 100 for each pumpunit 44,permits local control of the volume of fluid sprayed on the roll 12 atall points across the width thereof. Initially, in order to properlycalibrate theflcontrol assemblies 92, the limit screws 106 may berotated to their full of position corresponding to 0" on indicia portion110 which causes their corresponding pistons 68 to be pushed to the fullextent within their corresponding pump cylinders 46. By then setting thefollower bolt 100 for only extremely light engagement with theircorresponding eccentrics 90 during rotation of the latter, no dampeningfluid will be pumped to any of the sprayers 28. Then, by backing offselected limit screws 106 an amount desired depending upon the volume ofspray required for that particular location on roll 12, fluid will bepumped to the selected sprayers 28 as the plugs 62 are successivelycompressed and relaxed by their corresponding pistons 68. In thismanner, the control assemblies 92 may be accurately calibrated andcertain of the sprayers 28 may be redneered completely inoperable, whilestill others are displacing their full volumes of fluid.

It should also be appreciated that the nature of each control assembly92 contributes to its ease of installation and removal. By virtue of thefact that the fulcrum shaft 96 for each assembly 92 is disposedexteriorly of its arm 94, the latter may be easily removed by looseningbolt and screw 106, removing line 80, and pulling arm 94 free fromfulcrum 96 in either a downward or upward direction. Access is therebyeasily gained to the pumping plug 62 for service or replacement thereofas required.

Having thus described the invention, what is claimed as new and desiredto be secured by Letters Patent is: 1. In positive displacement fluidsupply apparatus:

a resilient pumping element having a fluid passage extendingtherethrough;

retaining structure precluding movement of the element in the directionof fluid flow through said passage and precluding outward expansion ofthe element transversely of said direction of fluid flow; and

mechanism for successively compressing and relaxing said element in saiddirection of fluid flow to thereby transversely constrict and expandsaid passage for pumping a metered volume of fluid therethrough.

2. In appararatus as claimed in claim 1, wherein said structure includesa stationary abutment against the element at one end of said passage andhaving a fluid outlet, said mechanism including a pistion reciprocableagainst the element at the opposite end of said passage and having afluid inlet.

3. In apparatus as claimed in claim 2, wherein said structure furtherincludes a housing receiving said element, said piston and saidabutment.

4. In apparatus as claimed in claim 2, wherein said piston is providedwith a valve for said inlet operable to close the latter duringcompression of the element by said piston and to open the inlet duringrelaxation of said element by the piston.

5. In apparatus as claimed in claim 4, wherein said abutment is providedwith a valve for said outlet operable to open thelatter duringcompression of the element by said piston and to close the outlet duringrelaxation of the element by said piston.

6. In apparatus as claimed in claim 1, wherein said passage has an inletend, said element being provided with a bubble way open to said inletend of the passage for preventing the collection of bubbles on saidelement externally of said passage.

7. In apparatus as claimed in claim 6, wherein said passage has anoutlet end, said way extending alongside said passage in opencommunication therewith toward said outlet end and terminating short ofthe latter.

8. In apparatus as claimed in claim 7, wherein said way progressivelydecreases in size and as said outlet end is approached.

9. In apparatus as claimed in claim 6, wherein said way tangentiallyintersects said passage on opposite sides of the latter at its inletend.

10. In appratus as claimed in claim 6, wherein said mechanism includes areciprocable piston having a fluid inlet for said passage of greatercross-sectional size than said inlet end of the passage, said wayextending, transversely of said passage, at least to the dimen-. sionallimit of said inlet.

11. In apparatus as claimed in claim 1, wherein is provided apneumatically-powered sprayer communicating with said passage forreceiving and nebulizing the metered volume of fluid displaced by saidelement.

12. In apparatus as claimed in claim 1, wherein said mechanism includesa reciprocable piston, drive means for operating the piston, and acontrol assembly between said driven means and the pistion for varyingthe stroke of the latter to thereby regulate the volume of fluiddisplaced by said element during each operating cycle.

13. In apparatus as claimed in claim 12, wherein said assembly includesa lever arm receiving power adjacent one end thereof from said drivemeans and transmitting said power adjacent its opposite end to saidpiston.

14. In apparatus as claimed in claim 13, wherein said assembly furtherincludes a variable limit stop for said arm.

15. In apparatus as claimed in claim 14, wherein said limit stop isdisposed for engagement with said arm adjacent said opposite endthereof.

16. In apparatus as claimed in claim 13, wherein said drive meansincludes an eccentric, said assembly further including a variablefollower for said eccentric on said arm adjacent said one end thereof.

'17. In apparatus as claimed in claim 13, wherein said arm is providedwith a power-transmitting rocker adjacent said opposite end thereofbearing against said piston during actuation of said arm.

18. In apparatus as claiemd in claim 13, wherein said arm is providedwith a fulcrum disposed externally thereof against which the arm ridesduring actuation, whereby the arm may be readily removed from thefulcrum.

19. In apparatus as claimed in claim 1, wherein is provided apneumatically-powered sprayer communicating with said passage forreceiving and nebulizing fluid displaced by said element, said structureincluding a housing about said element and a stationary abutment at oneend of said passage having a fluid outlet and a valve in said outlet,said mechanism including a reciprocable piston at the opposite end ofsaid passage having a fluid inlet and a valve in said inlet, saidmechanism further including a drive for said piston, swingable lever armbetween said drive and the piston for transmitting power from said driveto the piston, and an adjustable limit stop for said arm for varying thestroke of said piston to thereby control the volume of fluid displacedby said element to said sprayer, said inlet valve in the piston and saidoutlet valve in the abutment being operable to close and openrespectively during the compression stroke of said piston and to openand close respectively during the expansion stroke of the piston, saidelement being provided with a bubble way extending along said passage inopen communication therewith from said opposite end of the passagetoward saidone end thereof for directing bubbles into and through saidpassage.

20. In apparatus as claimed in claim 1, wherein is provided a pluralityof said elements, each provided with a said retaining structure and eachhaving a pneumaticallypowered sprayer associated therewith for receivingdisplaced fluid from the corresponding element and nebulizing the same.

21. In apparatus as claimed in claim 20, wherein said mechanism includesa reciprocable piston for each element, a drive shaft common to all ofsaid pistons for operationg the same, and a control assembly for eachpiston between said shaft and the corresponding piston for varying thelength of its stroke independently of the other pistons to therebypermit individual regulation of the fluid displaced to said sprayers.

22. In apparatus as claimed in claim 21, wherein each of said assembliesincludes a lever arm receiving power adjacent one end thereof from saidshaft and transmitting said power adjacent its opposite end to itscorresponding piston, each of said assemblies further including anadjustable limit stop for controlling the swinging of its correspondingarm.

23. In apparatus for repeatedly delivering small metered volumes ofdampening fluid to a printing system:

'a plurality of neumatically powered sprayers;

a series of individual pump units corresponding in number to saidsprayers for physically displacing fluid thereto for nebulizationthereby.

each of said units including a compressible, resilient pumping elementhaving a passage therethrough for moving fluid to the correspondingsprayer in response to the application of repeated compressive forces tothe element;

drive means for supplying power for compression to the pump units; and

a control assembly for each unit respectively operable to selectivelyvary the extent of compression and expansion of the correspondingpumping element independently of the other elements whereby to vary thevolume of fluid delivered to the corresponding sprayer.

24. In apparatus as claimed in claim 23, wherein said drive meansincludes a shaft common to said units, each of said assemblies includinga swingable lever arm between the shaft and the corresponding elementand a variable limit stop for said arm. 7

25. In apparatus as claimed in claim 23, wherein each of said units isprovided with structure precluding both movement of its element in thedirection of fluid flow therethrough and outward expansion of theelement transversely of the direction of fluid flow when a compressiveforceis applied to the element in said flow direction whereby toconstrict said passage and force fluid from the same.

1. In positive displacement fluid supply apparatus: a resilient pumping element having a fluid passage extending therethrough; retaining structure precluding movement of the element in the direction of fluid flow through said passage and precluding outward expansion of the element transversely of said direction of fluid flow; and mechanism for successively compressing and relaxing said element in said direction of fluid flow to thereby transversely constrict and expand said passage for pumping a metered volume of fluid therethrough.
 2. In apparatus as claimed in claim 1, wherein said structure includes a stationary abutment against the element at one end of said passage and having a fluid outlet, said mechanism including a piston reciprocable against the element at the opposite end of said passage and having a fluid inlet.
 3. In apparatus as claimed in claim 2, wherein said structure further includes a housing receiving said element, said piston and said abutment.
 4. In apparatus as claimed in claim 2, wherein said piston is provided with a valve for said inlet operable to close the latter during compression of the element by said piston and to open the inlet during relaxation of said element by the piston.
 5. In apparatus as claimed in claim 4, wherein said abutment is provided with a valve for said outlet operable to open the latter during compression of the element by said piston and to close the outlet during relaxation of the element by said piston.
 6. In apparatus as claimed in claim 1, wherein said passage has an inlet end, said element being provided with a bubble way open to said inlet end of the passage for preventing the collection of bubbles on said element externally of said passage.
 7. In apparatus as claimed in claim 6, wherein said passage has an outlet end, said way extending alongside said passage in open communication therewith toward said outlet end and terminating short of the latter.
 8. In apparatus as claimed in claim 7, wherein said way progressively decreases in size and as said outlet end is approached.
 9. In apparatus as claimed in claim 6, wherein said way tangentially intersects said passage on opposite sides of the latter at its inlet end.
 10. In appratus as claimed in claim 6, wherein said mechanism includes a reciprocable piston having a fluid inlet for said passage of greater cross-sectional size than said inlet end of the passage, said way extending, transversely of said passage, at least to the dimensional limit of said inlet.
 11. In apparatus as claimed in claim 1, wherein is provided a pneumatically-powered sprayer communicating with said passage for receiving and nebulizing the metered volume of fluid displaced by said element.
 12. In apparatus as claimed in claim 1, wherein said mechanism includes a reciprocable piston, drive means for operating the piston, and a control assembly between said drive means and the piston for varying the stroke of the latter to thereby regulate the volume of fluid displaced by said element during each operating cycle.
 13. In apparatus as claimed in claim 12, wherein said assembly includes a lever arm receiving power adjacent one end thereof from said drive means and transmitting said power adjacent its opposite end to said piston.
 14. In apparatus as claimed in claim 13, wherein said assembly further includes a variable limit stop for said arm.
 15. In apparatus as claimed in claim 14, wherein said limit stop is disposed for engagement with said arm adjacent said opposite end thereof.
 16. In apparatus as claimed in claim 13, wherein said drive means includes an eccentric, said assembly further including a variable follower for said eccentric on said arm adjacent said one end thereof.
 17. In apparatus as claimed in claim 13, wherein said arm is provided with a power-transmitting rocker adjacent said opposite end thereof bearing against said piston during actuation of said arm.
 18. In apparatus as claimed in claim 13, wherein said arm is provided with a fulcrum disposed externally thereof against which the arm rides during actuation, whereby the arm may be readily removed from the fulcrum.
 19. In apparatus as claimed in claim 1, wherein is provided a pneumatically-powered sprayer communicating with said passage for receiving and nebulizing fluid displaced by said element, said structure including a housing about said element and a stationary abutment at one end of said passage having a fluid outlet and a valve in said outlet, said mechanism including a reciprocable piston at the opposite end of said passage having a fluid inlet and a valve in said inlet, said mechanism further including a drive for said piston, swingable lever arm between said drive and the piston for transmitting power from said drive to the piston, and an adjustable limit stop for said arm for varying the stroke of said piston to thereby control the volume of fluid displaced by said element to said sprayer, said inlet valve in the piston and said outlet valve in the abutment being operable to close and open respectively during the compression stroke of said piston and to open and close respectively during the expansion stroke of the piston, said element being provided with a bubble way extending along said passage in open communication therewith from said opposite end of the passage toward said one end thereof for directing bubbles into and through said passage.
 20. In apparatus as claimed in claim 1, wherein is provided a plurality of said elements, each provided with a said retaining structure and each having a pneumatically-powered sprayer associated therewith for receiving displaced fluid from the corresponding element and nebulizing the same.
 21. In apparatus as claimed in claim 20, wherein said mechanism includes a reciprocable piston for each element, a drive shaft common to all of said pistons for operating the same, and a control assembly for each piston between said shaft and the corresponding piston for varying the length of its stroke independently of the other pistons to thereby permit individual regulation of the fluid displaced to said sprayers.
 22. In apparatus as claimed in claim 21, wherein each of said assemblies includes a lever arm receiving power adjacent one end thereof from said shaft and transmitting said power adjacent its opposite end to its corresponding piston, each of said assemblies further including an adjustable limit stop for controlling the swinging of its corresponding arm.
 23. In apparatus for repeatedly delivering small metered volumes of dampening fluid to a printing system: a plurality of neumatically powered sprayers; a series of individual pump units corresponding in number to said sprayers for physically displacing fluid thereto for nebulization thereby, each of said units including a compressible, resilient pumping element having a passage therethrough for moving fluid to the corresponding sprayer in response to the application of repeated compressive forces to the element; drive means for supplying power for compression to the pump units; and a control assembly for each unit respectively operable to selectively vary the extent of compression and expansion of the corresponding pumping element independently of the other elements whereby to vary the volume of fluid delivered to the corresponding sprayer.
 24. In apparatus as claimed in claim 23, wherein said drive means includes a shaft common to said units, each of said assemblies including a swingable lever arm between the shaft and the corresponding element and a variable limit stop for said arm.
 25. In apparatus as claimed in claim 23, wherein each of said units is provided with structure precluding both movement of its element in the direction of fluid flow therethrough and outward expansion of the element transversely of the direction of fluid flow when a compressive force is applied to the element in said flow direction wherebY to constrict said passage and force fluid from the same. 